1. Field of the Invention
This invention relates to a tandem, two-component mixer having an elongate dwell chamber. A reverse twist auger is located in the dwell chamber to provide continuous scraping of the dwell chamber wall and prevent a buildup of material therein. While the mixer of the present invention has a variety of uses, it is particularly well suited for the preparation of polyurethane gels filled with dispersed, discrete particles of aqueous solutions.
2. Description of the Prior Art
Tandem, two-component mixers are known to the mixing art and some of such mixers include a dwell chamber between the two mixing heads. Such prior art machines do not, however, have the ability to deliver a continuous stream of product where the reactants mixed in the machine gel rapidily. Such prior art mixers also permit a buildup of reactive material on the walls of the dwell chamber.
There are many chemical systems where it is desirable to provide a continuous product stream and where mixing control is important due to the reactivity of the various chemical substances. Cleanup of such systems is frequently difficult where the reactants have accumulated on the walls of the system or where adequate washing of the mixer components is prevented by improper mixer design.
One such chemical system is polyurethane gels formed by mixing a polyisocyanate prepolymer with an aqueous liquid. The prepolymer may be a prepolymer of an organic di-isocyanate and a polyether diol or triol, and the aqueous liquid may be water. Rapid mixing of the two components causes a gel to form and the final product desirably contains a homogeneous dispersion of discrete droplets throughout the gel. The final properties of such gels can be varied by the choice of starting materials and by the mixing techniques employed. The gel can have open or closed cells depending on these various factors and the nature of the cells can be adjusted by varying the solute in the aqueous solution. For example, the aqueous solution may contain colors, perfumes, fire retardents, electrically conductive materials and the like.
Gels such as those just described can be cast to a specific shape or can be formed in a mass for selected uses. The gels may also be extruded. Typical uses of such gels are in building construction, marking devices, prosthetic devices, medical devices, etc.
While the preparation of such gels is known, equipment has not been available for production of the gel on a continuous and reliable basis. Equipment required for this system must have the capability of efficiently mixing the reactants over a wide range of mixing conditions and must prevent gelled product from building up within the apparatus. Finally, the equipment must also be capable of being thoroughly washed to prevent permanent accumulations of product which would destroy the equipment or reduce its efficiency.